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Replacing one roof material with another

Archicentre has found, in the course of thousands of home inspections, that the biggest single cause of framing failures is the replacement of a lightweight roofing material, like metal with a heavy one, like tiles.

The extra weight stresses the roof frame and requires extra rafters and supporting framework. A roof which has bowed under such circumstances will be difficult to prop up as the additional timbers will simply hold the roof in the current position.

In some States, building approval is necessary before new roofing materials can be substituted, reducing the incidence of this fault.

A Room in the Roof?

Before re-roofing, and especially if you are re-framing, you should consider the possibility of creating a usable attic space. Archicentre's Design Concept Service is available to offer advice if you feel you need expert guidance.

On the question of costs, an upstairs renovation often compares well with extending out, provided that the house does not require too many structural modifications to cope with the added weight and repositioning of framing timbers, bearing in mind, the ground floor space lost to the interconnecting stairs.

Houses with a steeper pitch stand to gain more space, and these days liberalised building regulations allow greater freedom with such practical design features as skylights or sky windows.

Re-Roofing – Choosing what materials to use

Metal Roofing

• Metal roofing is more common nowadays than in past decades.
• Its advantages compared to tiles are design flexibility and ease of installation.
• Metal roofing is the best option when the pitch (slope) of the roof is less than fifteen degrees from horizontal.
• The disadvantages of metal roofing are the greater susceptibility to weathering and industrial pollution, and if the surface is scratched, corrosion can set in almost immediately.
• It can also be noisier in the rain than tiles, but to some people that is an attraction rather than a distraction. An insulating blanket fixed to the underside of the roof would reduce noise.

Concrete Tiles

• Concrete tiles were previously much maligned as a roof material.
• Over the years they lost both tensile strength (in other words, the maximum tension the tiles can withstand without tearing) and colour. Today, however, they are enjoying a come-back due to technological improvements.
• Concrete tiles are now stronger and more colour-fast than before and, significantly, 25-30% cheaper than their terracotta equivalents. They also offer a wider selection of colours and profiles.

Terracotta Tiles

• Terracotta tiles, as well as being more expensive, are slightly heavier than concrete.
• They have a reputation for their long-life qualities, and are the traditional favourites. Terracotta tiles are available in a number of different profiles and colours.

Slate Roofs

Slate roofs offer a high standard of weatherproofing, look good, but are very expensive. Imitation slate is available in concrete tiles, fibre cement sheets and now there is even a terracotta equivalent.

Pressed Metal Tiles

Pressed metal tiles actually cost more than terracotta tiles but are lightweight, leading to savings in transport and framing costs.

Stone-chip Metal Tiles

Metal tiles with real stone chips bound in acrylic may be more expensive than terracotta in most cases. But costs may be saved on timber framing when cladding a new house because of the tiles' lighter weight.

Shingles

Shingles can be made of timber or fibrous cement. Generally both last well and have good insulating properties. However, availability can be a problem.